1. Structural Classification of the Nervous System
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
Nerves outside the brain and spinal cord

2. Functions of the Nervous System
Sensory input – gathering information
To monitor changes occurring inside and outside the body
Changes = stimuli
Integration
To process and interpret sensory input and decide if action is needed
Motor output
A response to integrated stimuli
The response activates muscles or glands

4. Nervous Tissue: Neurons
Neurons = nerve cells
Cells specialized to transmit messages
Major regions of neurons
Cell body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell body

5. Neuron Anatomy
Cell body – contains organelles. Neurons lack centrioles and are incapable of mitosis
Nissl substance – specialized rough endoplasmic reticulum. Attached ribosomes. Function to synthesize vital protein molecules
Neurofibrils – intermediate cytoskeleton that maintains cell shape
Extensions outside the cell body
Dendrites – short, branched receptive surfaces that conduct impulses toward the cell body
Axons – long, usually singular and conduct impulses away from the cell body

6. Axons and Nerve Impulses
Axons end in axonal terminals
Axonal terminals contain vesicles with neurotransmitters
Axonal terminals are separated from the next neuron by a gap
Synaptic cleft – gap between adjacent neurons
Synapse – junction between nerves

7. Nervous Tissue: Support Cells (Neuroglia)
1. Astrocytes
Abundant, star-shaped cells
Brace neurons
Form barrier between capillaries and neurons
Control the chemical environment of the brain
Figure 7.3a

8. 2. Microglia 3. Ependymal cells Spider-like phagocytes
Dispose of debris
3. Ependymal cells
Line cavities of the brain and spinal cord
Circulate cerebrospinal fluid

9. Nervous Tissue: Support Cells
4. Oligodendrocytes
Produce myelin sheath around nerve fibers in the central nervous system
Figure 7.3d

10. Nervous Tissue: Support Cells
5. Satellite cells
Protect neuron cell bodies
6. Schwann cells
Form myelin sheath in the peripheral nervous system

12. Functional Classification of Neurons
Sensory (afferent) neurons
Carry impulses from the sensory receptors
Cutaneous sense organs
Proprioceptors – detect stretch or tension
Motor (efferent) neurons
Carry impulses from the central nervous system

13. Interneurons (association neurons)
Found in neural pathways in the central nervous system
Connect sensory and motor neurons

14. Structural Classification of Neurons
Multipolar neurons – many extensions from the cell body. Characteristic of Motor Neurons
Figure 7.8a

15. Structural Classification of Neurons
Bipolar neurons – one axon and one dendrite. Found only associated with special senses. (Olfactory, vision)
Figure 7.8b

16. Structural Classification of Neurons
Unipolar neurons – have a short single process leaving the cell body. Sensory Neurons
Figure 7.8c

17. Nerve Impulses
The surface of the nerve cell membrane is polarized due to unequal distribution of ions on either side of the membrane
When nerve cells are at rest there is a greater concentration of Na+ ions outside the membrane and a greater concentration of K+ ions inside the membrane. (Rest Potential)
This arrangement of ions gives the outside of the membrane a positive charge with respect to the inside.

19. A stimulus causes a change in permeability in a region of the membrane
Na+ ions rush into the cell and K+ ions rush out depolarizing the region of the membrane
This region of depolarization is an Action Potential
An action potential in one region stimulates adjacent regions to depolarize and the action potential moves away from the point of stimulus
This moving action potential is a Nerve Impulse
The membrane is repolarized in 1/1000 sec. by active transport

20. Continuation of the Nerve Impulse between Neurons
Impulses are able to cross the synapse to another nerve
Neurotransmitter is released from a nerve’s axon terminal
The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter
An action potential is started in the dendrite

22. Reflexes
Reflex – automatic, unconscious, and involuntary responses to stimuli
Simplest nerve pathways
Autonomic Reflexes – involve contractions of smooth muscles
Somatic Reflexes – involve contractions of skeletal muscles
Help maintain homeostasis by controlling: body temperature, heart rate, breathing rate, blood pressure and digestive activities

23. Patellar Reflex – (knee-jerk reflex) Employs only two neurons
Patellar Reflex – (knee-jerk reflex) Employs only two neurons. Helps maintain posture
Also swallowing, sneezing, coughing, vomiting are reflexes

25. Withdrawl Reflex

26. Withdrawl Reflex
1. Receptor – sets up a nerve impulse when something painful is touched
2. Sensory Neuron – carries the impulse to the spinal cord
3. Interneuron – conducts the impulse from the sensory to a motor neuron
4. Motor Neuron – conducts the impulse to the effector
5. Effector – responds to stimulation by muscle contraction